Isolation Of Oil-rich Microalgae For Fixation Of High Concentration Of Carbon Dioxide And Lipid-accumulation Process Biochemistry Study

In order to reduce production cost and obtain oil-rich microalgae strains for industrial application, this research was conducted to collect and screen some microalgae for carbon dioxide fixation and biodiesel production. And, Sudan black B staining method was found and optimized to qualitatively and quantitatively analyze microalgal lipids in situ. The effects of nitrogen concentration on the growth and content of lipids, intracellular proteins, and soluble sugar of two microalgae were studied. It’s significant to lay the foundation for industrial fuel gases bio-fixation and development of biomass energy. The main contents were shown as following:(1) Isolation and purification of samples collected from Gansu province were conducted using BG-11medium. Two strains with potential of biodiesel production and fixation of CO2in industrial flue-gases based on their good growth properties and named as Chlorella pyrenoidosa XJO1and Chlorella sorokiniana XJ02based on morphology examination,18S rRNA and internal transcribed space (ITS-2) sequences analysis (Sequences of18S rRNA and ITS-2of the two isolates were submitted to Genbank with accession numbers KC416209and KC416206for XJ01, and KC416208and KC416207for XJ02, respectively). They displayed high biomass concentration, high lipids productivity and carbon dioxide tolerance ability when they were cultivated with20%CO2. The maximum biomass concentration, lipid content and CO2fixation rate for C. pyrenoidosa XJ01in12days cultivation were1.81g/L,31.5%and0.28g/L/d, respectively. And, those for C. sorokiniana XJ02were1.52g/L,40.13%and0.24g/L/d, respectively. The analysis of fatty acid compositions of the two strains showed a predominance of of oleic acid (C18:1) and considerable amounts of palmitic acid (C16:0) stearic acid (C18:0), linoleic acid (C18:2) and alphalinolenic acid (C18:3). Therefore, They have the potential ability to sequestrate industrial fuel gases and produce biodiesel. (2) Sudan black B staining method was found and optimized to qualitatively and quantitatively analyze microalgal lipids in situ. The results indicate that Sudan black B staining method can be regarded as a feasible method for analysis of lipids in microalgae in situ. And, Lipid in microalgal cells started to accumulate from interim of logarithmic phase and reached highest value at interim of stationary phase and then began to decrease, and high CO2level (20%) was favorable for accumulation of lipids, which were consistent with the results of oil-droplet images obtained by microscope.(3) The effects of different nitrogen concentration on the growth and content of intracellular lipid, protein and soluble sugar of two microalgae were conducted. The results showed that lower nitrogen concentration accelerated growth of two microalgae at the early stage of the cultivation, but the lower nitrogen concentration affected the microalgal total biomass concentration, and dramatically improved lipids accumulation, and the lipid contents of C. pyrenoidosa XJ01and C. sorokiniana XJ02were49%and60%, respectively, under the lower nitrogen concentration and20%CO2.